1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, or the like and, more particularly, to an image forming apparatus having a heat fixing means.
2. Related Background Art
In a conventional image forming apparatus having a heating fixing means, a halogen heater, a ceramic heater, or the like is energized by a commercial power supply.
Energization to the heater is controlled, so that the temperature of a heating member such as a heat roller is maintained a predetermined fixing temperature.
However, when the voltage output from the commercial power supply drifts due to a power supply circumstance of the place of use of the image forming apparatus, the heat generation amount of the heater is changed, and the heating member cannot be accurately temperature-controlled, thus adversely affecting image quality. In particular, since the ceramic heater is a pure resistor, its electric power changes according to the square of the input voltage. Furthermore, in an apparatus, which employs a heating member having a small heat capacity to meet a requirement for shortening the image formation time, the temperature gradient tends to increase, and a change in temperature caused by the voltage drift is increased.
In order to prevent the change in temperature caused by the power supply voltage drift, a circuit 802 for detecting a power supply voltage may be connected to a power supply circuit 801 so as to detect an input voltage.
However, this circuit requires a special-purpose transformer 803 for detecting a voltage, resulting in an increase in apparatus size.